Suspended drive axle and agricultural tractor with same

ABSTRACT

A suspended drive axle and agricultural tractor having same including a central housing having inboard final drives and left and right axle housing suspended therefrom by upper and lower control arms with axle shafts extending outwardly therefrom to which wheel and tire assemblies are mounted. A constant velocity universal joint is provided between the inboard final drives and the axle shafts. The universal joint having a pair of journal members and a coupling yoke that radially surround the drive and driven yokes of the joint whereby the axial length of the universal joint is minimized to enable the wheels to be located on the axle shafts at 60 inch tread spacing. This allows the drive axle to be used on a row crop tractor without altering the structure of the vehicle from a conventional row crop tractor whereby the characteristics of a row crop tractor are maintained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an agricultural tractor with asuspended drive axle and in particular to a tractor having anindependent rear suspension.

[0003] 2. Description of the Related Art

[0004] An agricultural tractor is intended primarily for off-road usageand is designed primarily to supply power to agricultural implements. Anagricultural tractor propels itself and provides a draft force in thedirection of travel to enable an attached, soil engaging, implement toperform its intended function. Furthermore, an agricultural tractor mayprovide mechanical, hydraulic and/or electrical power to the implement.Agricultural tractors must be designed with sufficient normal force,down force, acting on the drive wheels to produce the needed draftforce. Typically, in a two-wheel drive tractor, this results in avehicle having rear drive wheels that are larger then the front wheelsto accommodate the required normal force on the rear drive wheels.Agricultural tractors differ from cargo carrying vehicles, such aspickup trucks and semi-truck tractors, in that trucks do not need toproduce a continuous draft load. A truck produces a draft load onlyduring periods of acceleration and deceleration and relies on the weightof the cargo carried by the drive wheels to produce the draft load.

[0005] The productivity of an agricultural tractor can be increased byfaster travel speeds in the field and on the road. A significantlimiting factor to the travel speed of an agricultural tractor is thecomfort of the operator when travelling over rough surfaces. A typicaltractor has an integrated structure in which the rear axle and hitch areintegrated into one unit and forms a part of the vehicle framestructure. In such a case, there is no suspension between the rear axleand the tractor frame. Tire deflection alone provides a cushioningbetween a rough surface and the tractor frame. Seat suspensions and cabsuspensions have also been used with limited success to improve operatorcomfort.

[0006] The front axle, which may or not be driven, is typically a beamaxle pivotally mounted to the tractor for limited rotation about alongitudinal axis. Suspended front axles have been developed fortractors such as that shown in U.S. Pat. No. 5,879,016. There, a rigidbeam axle having outboard planetary final drives is suspended from thetractor frame. Suspended front axles have provided improved comfort foroperators.

[0007] However, due to the lack of a rear suspension, significant loadscaused by an uneven terrain are still transmitted to the vehicle frameand to the vehicle operator. Tractor speed, particularly in the field,is limited by the jostling of the operator. Operator fatigue occurssooner the more the operator is jostled in the cab. Thus there exists aneed for a rear suspension in an agricultural tractor to reduce operatorfatigue, thereby allowing the operator to productively work longer hoursand/or to operate at a faster travel speed.

[0008] One attempt at providing a rear suspension is shown in U.S. Pat.No. 5,538,264. There, a rear beam axle is suspended from the tractorframe. To include the suspension, the tractor design deviates from aconventional row crop tractor of comparable power in at least thefollowing respects: 1) the rear axle is equipped with outboard finalplanetary drives instead of inboard final drives; 2) the tractor isequipped with four equal sized tires, all smaller than the large reartires on a conventional row crop tractor of comparable power; and 3) therear axle is moved substantially rearward relative to the tractor cab,as compared to a conventional row crop tractor.

[0009] The outboard final drives limit the adjustability of the treadwidth and prevent the tread width from being infinitely adjustable alongthe axle. Only discrete changes in the tread width are available throughdifferent wheel and rim configurations. Of the commercially availabletractors embodying the invention of the U.S. Pat. No. 5,538,264, only tolowest power tractors are available with a tread width as narrow as 60inches. The smaller tires have a lower load carrying capability,resulting in less traction. The rearward location of the rear axlerelative to the cab interferes with visibility of the hitch by theoperator. An additional disadvantage of this design is that the tractorhitch is carried by the suspended axle, and is thus part of the unsprungmass. The lack of a suspension for the hitch results in towed implementsfollowing the vertical motion of the tires and axle as opposed to themore steady movements of the tractor frame. A further disadvantage isthat the beam axle does not enable an independent suspension.

[0010] As a result of all the differences between the tractor of the'264 patent and a conventional row crop tractor, the '264 tractor doesnot achieve the same level of performance of a comparable power row croptractor. The tractor of the '264 patent does allow increased travelspeeds, both in the field and on the road, but at a significant ‘cost’in terms of performance in the field. The tractor of the '264 patent isdesigned more for use as a hauling vehicle and for road transport thanfor field work pulling a soil engaging implement. Accordingly, therestill exists a need for a row crop tractor having a rear suspensionwhile maintaining the performance and operational characteristics of arow crop tractor of comparable power with a rigid, non-suspended, reardrive axle.

[0011] A row crop agricultural tractor is designed to operate in thefield with the tread width set for the wheels to travel between rows.Conventionally, this has meant a tractor with a tread width as narrow as60 inches, enabling the tractor to straddle two crop rows spaced 30inches apart. The tread width is adjustable so that it can be customizedfor a particular farm application with row spacings other than 30inches. Infinite adjustability can be provided by wheel hubs that clampto an axle at any location along a length of the axle. This type ofadjustment mechanism necessitates an inboard planetary final drive.Other adjustment mechanisms involve changing the wheel rim and discconfiguration to change the tread width.

[0012] Small row crop tractors such as the JOHN DEERE 6010 Seriestractors have power ratings ranging between 49 kW to 71 kW (65-95 hp).Large row crop tractors such as the JOHN DEERE 8010 series tractorsrange in power from 123 kW to 175 kW (165 to 235 hp). These tractors allhave inboard final drives to enable an infinitely adjustable treadwidth. In the JOHN DEERE 8010 series tractors, the width of the reardifferential case, between the inboard planetary final drives, is 665 mm(26.2 inches). A rear suspension must be packaged outboard of the finaldrive and inboard of the wheel mounting equipment at a 60 inch treadwidth to maintain the same row-crop capabilities in a suspended tractorof this size as in the non-suspended tractor.

SUMMARY OF THE INVENTION

[0013] The tractor of the present invention maintains the transmission,rear differential and inboard planetary final drive assembly of acomparable sized row crop tractor without a rear suspension. The tractorof the present invention provides left and right suspended axle housingseach coupled to the final drive housing by a pair of suspension controlarms and one or more spring assemblies. Left and right axle shafts arecarried by the suspended axle housings and are coupled to the finaldrive outputs by a constant velocity joint, such as a double cardanjoint. The constant velocity joint is configured with the end of thefinal drive output closely spaced from the inboard end of the axleshaft. The remainder of the joint, the two journal members and theconnecting link, are larger in diameter and radially surround the shaftends. This arrangement of the joints reduces the axially length of theuniversal joint to a minimum, to enable the suspension to be packaged inthe narrow space available. A relatively large constant velocity jointis needed since it is downstream of the final drive, thus transmitting alarge torque.

[0014] The fixed axle housing of a non-suspended axle, which extendsoutward from the final drive, is replaced by an inner suspensionhousing, fixed to the differential case. The upper and lower controlarms extend from the inner suspension housing to the suspended axlehousing. The axle shaft is supported by the axle housing and extendsoutwardly therefrom. Wheels are mounted to the left and right axleshafts in the same manner as in a non-suspended axle, providing infinitetread width adjustability. Dual tire capability is also maintained. Oneor more spring assemblies extending between the inner suspension housingand the axle housing allow the axle housing to resiliently move up anddown relative to the tractor frame. By mounting the suspension to thedifferential case in place of the fixed axle housing of a non-suspendedaxle, a suspension axle is produced with only a few modifications to anon-suspended axle. As a result, a manufacturer can economically offerboth suspended and non-suspended tractor models.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side view of a row crop tractor.

[0016]FIG. 2 is a rear perspective view of a non-suspended rear driveaxle for the tractor of FIG. 1.

[0017]FIG. 3 is a rear perspective view of the non-suspended rear driveaxle shown in FIG. 2 with the left side axle housing removed toillustrate the inboard planetary final drive.

[0018]FIG. 4 is a rear view of the left side suspension system of thepresent invention mounted to the differential case of the rear axleshown in FIGS. 2 and 3.

[0019]FIG. 5 is a front view of the left suspension system shown in FIG.4.

[0020]FIG. 6 is a cross sectional view through the connecting link asseen from substantially the line 6-6 of FIG. 5

[0021]FIG. 7 is sectional view through the suspension upper control arm.

[0022]FIG. 8 is sectional view through the suspension lower control arm

[0023]FIG. 9 is a fragmentary view of the ball joint attachment of theupper control arm to the outer suspension housing.

[0024]FIG. 10 is a cross sectional view of the universal jointconnecting the planetary final drive to the axle shaft.

[0025]FIG. 11 is an exploded perspective view of the universal jointshown in FIG. 11.

[0026]FIG. 12 is an elevational view of an alternative embodiment of theleft suspension system including a rear wheel steering cylinder.

[0027]FIG. 13 is an exploded perspective view of an exemplary treadwidth adjustment mechanism for a wheel.

[0028]FIG. 14 is a simplified electro-hydraulic schematic.

[0029]FIG. 15 is a side view of an articulated four-wheel drive tractor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] An agricultural row crop tractor 10 is shown in FIG. 1. Thetractor 10 includes a frame 12, front tire and wheel assemblies 14, reartire and wheel assemblies 16 and an operator station 18, including acab. A hood 20 covers an engine 22.

[0031] With reference to FIGS. 2 and 3, a non-suspended rear drive axleassembly 26 for the tractor 10 is shown. The rear drive axle assemblyincludes a differential case 28 mounted to a transmission housing 30 andlocated rearward thereof. The differential case and transmission housingare part of the powertrain and are rigidly secured to the tractor frame12 and become a part of the frame 12. The differential case is thus partof the tractor structure. A three-point hitch (not shown) is mounted tothe upper portion 32 of the rear face of the differential case while aPTO housing (not shown) is mounted to the lower portion 34 of the rearface. The rearwardly extending shaft 36 drives the PTO.

[0032] Left and right axle housings 40, 42 support axle shafts 44, 46extending to the left and right. The rear tires 16 are mounted to theaxle shafts 44,46. The left axle housing 40 is mounted to thedifferential case through a plurality of bolts 48. The axle housing 40is bolted to the ring gear 50 of the left inboard planetary final drive52 (FIG. 3). The planetary final drive includes a driven sun gear 54, aplurality of planet gears 56 and the stationary ring gear 50 that formspart of the differential case. A planet carrier 172, shown in FIGS. 10and 11, supports the planet gears 56. The carrier is splined to the axleshaft 44 to drive the axle shaft as the planet gears 56 travel aroundthe ring gear 50. A right planetary final drive assembly includes thesame components as the left planetary final drive assembly 52. Only thering gear 58 of the right final drive is shown.

[0033] The Suspension

[0034] The suspension of the present invention is illustrated in FIG. 4where only the left side is shown. A substantially identical suspensionis provided on both the left and right sides of the tractor. Theassembly 60 includes an inner suspension housing 62 bolted to the finaldrive ring gear 50 in place of the axle housing 40 of the non-suspendedaxle shown in FIG. 2. Upper and lower control arms 64, 66 are mounted tothe inner suspension housing 62 for pivotal motion about upper and loweraxes 68, 70 (FIGS. 7 and 8). At their outer ends, the control armssupport an axle housing 72 through upper and lower ball joints 74, 76.The couplings of the upper and lower control arms to the innersuspension housing and to the axle housing are shown in greater detailwith reference to FIGS. 7 and 8.

[0035] The differential case, the final drive ring gears and the leftand right inner suspension housings 62 form a ridged body also referredto herein as a central housing. The central housing is attached to thetractor frame and is part of the frame structure to which other vehiclecomponents, such as the cab, are mounted.

[0036] An axle shaft 80 is rotatably carried by the axle housing 72 andextends laterally outwardly therefrom. The rear wheels and tires 16 ofthe tractor are mounted to the axle shaft 80 as described below.Vertical loads are transmitted between the inner suspension housing andthe axle housing by front and rear hydraulic cylinders 82, 84. Thecylinders 82, 84 are each coupled to the inner suspension housingthrough a clevis 86 while the cylinder rods 88 are each coupled to theaxle housing 72 by a clevis 90. The devises 86, 90 can be integral withthe inner suspension housing and the axle housing or separate itemsattached thereto.

[0037]FIG. 4 shows the suspension 60 from the rear with the suspensioncomponents in a nominal, or centered, position relative to the tractorframe. FIG. 5 shows the suspension from the front with the rods 88 ofthe cylinders 82, 84 extended. This places the axle shaft 88 in alowered position relative to the chassis as would occur when the lefttire encountered a rut or depression in the ground surface. The axleshaft 80 is lower than the axis 170 of the planet carrier 172. The upperand lower control arms 64, 66 are downwardly inclined, as is theuniversal joint 150.

[0038] The axle housing 72 is coupled to the distal ends of the upperand lower control arms by upper and lower ball joints 74, 76,respectively, as described in more detail below. The ball joints allowthe axle housing 72 to pivot about a generally upright axis passingthrough the ball joints. To prevent this pivoting motion and keep therear tires aligned with the tractor fore and aft longitudinal axis, afixed length connecting link 96 is coupled to the inner suspensionhousing and the axle housing on the front side of the suspension (FIGS.5 and 6). The connecting link 96 prevents pivotal motion of the axlehousing 72 about the upright axis passing through the ball joints 74,76.

[0039] The structure and attachment of the connecting link 96 is shownin FIG. 6. The link 96 is made of two halves 91, 92 that surround thefront hydraulic cylinder 82. The halves are fastened to pivot balls 93by shoulder bolts 94. The pivot balls 93 are fixed in sockets inmounting studs 95. The studs 95 are threaded into the inner suspensionhousing 62 and the axle housing 72. The ball and socket connectionsenable the connecting link to pivot relative to the inner suspensionhousing and the axle housing as the axle housing 72 moves up and down.

[0040] The upper control arm 64 is shown in greater detail withreference to FIG. 7. The inner end of the control arm is forked, forminga clevis that surrounds a mounting boss 98 of the inner suspensionhousing 62. A pivot pin 100 is press fit into the boss 98. A bearing set102 in each fork of the clevis surrounds the pivot pin 100. Snap ringgrooves 104 are formed in each fork of the clevis to receive a snap ringto retain the bearings. The pivot pin 100 defines the upper axis 68.

[0041] The upper and lower ball joints 74, 76 at the outer ends of thecontrol arms are shown with reference to FIGS. 7, 8, and 9. The balljoints include a spherical socket 132 in the control arms at the distalends thereof. A ball stud 134 has a spherical ball portion 135 andoppositely extending studs 136, 137. The ball stud 134 is retained inthe socket 132 by a treaded collar 138 in a known manner for a balljoint.

[0042] A pair of identical mounting blocks 140 (FIG. 9) attaches theball studs to the axle housing 72. The mounting blocks each have a crossbore 142 that receives one stud of the ball stud 134. Each mountingblock 140 has a slot 144 extending outward from the bore 142. Throughbores transverse to the cross bore 142 receive bolts 146 that attach themounting blocks to the axle housing 72. The bolt 146 passing through theslot 144 clamps the mounting block onto the stud to fix the ball stud134 from rotation. The ball stud, together with the mounting blocks andouter suspension housing, is allowed to pivot within the socket 132 atthe end of the control arm. An internal passage 148 in the ball stud 134allows the ball joint to be lubricated. A grease fitting, not shown, isplace in the passage 148 at the end of the stud 136.

[0043] The lower control arm 66 is shown in greater detail withreference to FIG. 8. The lower control arm is generally Y shaped havingfront and rear legs 112, 114 separately attached to the inner suspensionhousing 62. The front leg 112 has a bore 115 therein which receives adoubled tapered roller bearing set 116 and seals 117. A mounting pin 118extends through the bearing set and is held in the bearings by ashoulder 119 at one end of the pin 118 and a nut 120 at the other end. Apair of bolts 121 fixes the pin 118 to the inner suspension housing 62.

[0044] The rear leg 114 is forked, forming a clevis 122 that surrounds amounting boss 123 of the inner suspension housing 62. A pivot pin 124, abushing 126 and a needle bearing set 127 are mounted in a bore 128 inthe boss by a bolt 129. The end of the bolt 129 is threaded into oneside of the clevis 122. The two pivot couplings of the lower control armto the inner suspension housing define the lower axis 70. The outerdistal end of the lower control arm carries the ball joint assembly 76which is substantially identical to the upper ball joint assembly 74described above.

[0045] The mounting of the axle shaft 80 into the axle housing is shownin greater detail with reference to FIG. 10. The axle housing 72 has aninwardly projecting center hub 160 that carries inner and outer taperedroller bearings 162, 164. The axle shaft 80 is rotatably supported inthe axle housing 72 by the bearings 162, 164. Seals 166, 168 seal thebearings. The seal 168 engages a ring 169 on the axle shaft 80.

[0046] The left and right sides of the suspension are mechanicallyseparate from one another whereby one side can move without mechanicallycausing the other side to move. As described below, in the preferredembodiment the hydraulic cylinders are cross-linked left to right suchthat movement on one side will have an effect on the opposite side. Ifdesired, the left and right cylinders can be separated from one another.

[0047] The Universal Joint

[0048] Rotational power is transmitted from the planetary final drive tothe axle shaft 80 through a constant velocity universal joint 150. Thejoint 150 is located between the upper and lower control arms andbetween the front and rear hydraulic cylinders 82, 84. The constantvelocity joint 150 is shown in detail in FIGS. 10 and 11. The planetcarrier 172 is coupled to a joint inner yoke 174 by a retaining disk 176and bolt 178. The inner yoke 174 further has an external spline 180 thatis fitted into the internal spline 182 of the planet carrier. The inneryoke 174 is supported in an outwardly projecting hub 184 of the innersuspension housing by a double tapered roller bearing set 186. The inneryoke 174 projects radially outward at the end of the hub 184 of theinner suspension housing and forms a reverse bend to extend axiallyinward, forming a collar 196 that surrounds the hub 184 of the innersuspension housing. The collar 196 extends axially inward beyond theouter edge of the bearing set 186.

[0049] The axle shaft 80 is splined to an outer yoke 190 and is alsoretained therein by a retaining disk 192 and bolt 194. The outer yoke190 likewise projects radially outward and then forms a reverse bend toextend axially outward, forming a collar 198 surrounding the hub 160 ofthe axle housing 72. The collar 198 extends outward beyond the bearing162. The inner and outer yokes 174, 190 are also referred to herein asdrive and driven yokes respectively.

[0050] The constant velocity joint 150 is designed to locate the outeryoke 190 as close as possible to the inner yoke 174 to minimize theaxial length of the constant velocity joint. Doing so provides room forthe bearing support for the axle shaft 80 and enables the suspensionassembly to be packaged within the narrow space available. The bearingrequirements for supporting the axle shaft 80 and still enable a minimum60 inch tread width results in little axial distance between the bearing162 of the axle shaft 80 and the bearing set 186 of the inner yoke 174.The yokes 174, 190, with collars that wrap around the hubs of the innersuspension housing and the axle housing, allow the remaining componentsof the constant velocity joint to be located radially outward from thedrive and driven shafts. This is in contrast to a typical double cardanuniversal joint where the components are arranged axially in line withthe drive and driven shafts. In a preferred embodiment, the outboardface 175 of the inner yoke 174 is space from the inner face 191 of theouter yoke 190 by less than 2.54 cm (1 inch).

[0051] The collar 196 of the inner yoke 174 has two radially outwardlyprojecting studs 200, spaced diametrically opposite one another. Thestuds 200 define a first joint pivot axis 202. Likewise, the collar 198of the outer yoke has two radially outwardly projecting studs 204,spaced diametrically opposite one another and defining a third jointpivot axis 206. The studs 200 and 204 and the axes 202 and 206 areparallel to one another.

[0052] The joint 150 further includes axially inner and outer annular“cross” or ring members 210, 212. The ring members are used in place ofthe cross-shaped members in a typical cardan universal joint. The ringor cross members are also referred to herein generically as “journal”members. The ring members 210, 212 are each formed of two half members210 a, 210 b, and 212 a, 212 b. The half members are bolted together onradial planes by a plurality of bolts 214, only one set of which isshown in FIG. 11. When assembled, the ring members form bores 220 thathold bearing cups. A pair of bearing cups 216 are placed on the studs200 of the inner yoke while a pair of bearing cups 218 are placed on thestuds 204 of the outer yoke 190 to enable the ring members to pivotabout the axes 202 and 206 respectively.

[0053] A two piece coupling yoke 222 has two halves 222 a, 222 b. Thetwo halves are joined together on an axial plane by a plurality of bolts224. The coupling yoke has four radially inwardly projecting studs, twoaxially inner studs 226 and two axially outer studs 228. The inner studs226 define a second joint pivot axis 232 while the outer studs 228define a fourth joint pivot axis 234. The inner studs 226 are capturedin bores 238 formed by the inner ring member 210 while the outer studs228 are captured in bores 240 in the outer ring member 212. Bearing cups242, 244 are placed over the inner and outer studs 226, 228respectively. Grease fittings 246 are provided for each of the bearingcups.

[0054] The joint 150 is a double cardan universal joint with the ringmembers connected by the coupling yoke. The suspension control armscontrol the movement of the axle housing relative to the innersuspension housing and keep the axis 81 of the axle shaft 80 generallyparallel to the axis 170 of the inner yoke 174. This keeps the pivotangle at each of the ring members equal to one another so that aconstant, or near constant, velocity output is achieved.

[0055] The universal joint is made axially compact by forming the crossmembers as rings to move the ring members and coupling yoke radiallyoutward, to surround the drive and driven shafts. In this case, thebearing support for the axle shaft is inside the U-joint, axiallybetween the two ring members. This enables the provision of a hightorque capacity joint, while minimizing the axial length of the joint.High torque carrying capability is required since the joint is locatedoutboard, or downstream, of the planetary final drive. This arrangementof a U-joint relative to the drive and driven shaft bearings is madepossible by the configuration of the yokes, forming a collar thatsurrounds the hubs mounting the respective bearings.

[0056] It may also be possible to configure the universal joint with thejournal members and the coupling yoke radially inward of the inner andouter yokes. Such an arrangement would still have bearings locatedaxially between the joint pivot axes.

[0057] The first and second joint pivot axes-202, 232 are in a commonplane that is inboard of the outer edge of the bearing set 186.Likewise, the third and fourth joint pivot axes 206, 234 are in a commonplane that is outboard of the inner edge of the bearing 162.

[0058] Rear Wheel Steering

[0059] An alternative embodiment of the invention is shown in FIG. 12.The connecting link 96 described above has been replaced with ahydraulic cylinder 250 having a cylinder rod 252. The cylinder 250 islocated forward of suspension cylinder 82 which passed through the fixedlength connecting link 96. The rod 252 can be extended or retracted tochange the distance between the inner suspension housing and axlehousing forward of the axle shaft 80. This allows the axle suspensionhousing to rotate about the upright axis defined by the upper and lowerball joints 74, 76. This turns the rear wheels and tires, providing rearwheel steering to the tractor.

[0060] Tread Width Adjustment

[0061] The tread with adjustment mechanism for the wheels is describedwith reference to FIG. 13. The axle shaft 80 supports an adjustablewheel assembly that includes a wheel hub 254. The wheel hub 254 has atapered bore 256 large enough to accommodate the outside diameter of theshaft 80 and to provide an annular tapered bore in which upper and lowertapered flanged sleeves 260, 262 can be received in a wedging actionwithin the tapered bore 256. The upper tapered flanged sleeve 260 has aradially extending, semi-circular flange 264 and a semi-conical, axiallyextending portion 266. The lowered tapered flange sleeve 262 is of thesame configuration as the upper sleeve 260, having a radially extending,semi-circular flange 268 and a semi-conical, axially extending portion270. Together, the semi-conical portions 266, 270 provide afrusto-conical mounting surface for the hub 254. The sleeves 260, 262have semi-cylindrical inner surfaces which, when tightened intoposition, encompass and clamp to the axle shaft 80.

[0062] An annular collar 272 is slidably positioned on the axle shaft 80between the wheel hub 254 and the sleeves 260, 262 to maintain the wheelin a proper attitude and prevent binding after the sleeves 260, 262 havebeen loosened from the tapered bore 256. The hub 254 is provided with aplurality of angularly spaced threaded bolt bores 274. Bolts 276 arereceived within the bolt bores 274. The semi-circular flanges 264, 268of the sleeves 260, 262 are provided with a plurality of angularlyspaced bolt holes 278. When the bolts 276 are treaded into the bores 274in the hub 254, the semi-conical portions 266, 270 are drawn into thetapered bore 256 and are clamped to the axle shaft 80. Any variety ofclamping arrangements can be used with the axle shaft 80 as are wellknown in adjusting the tread width of an agricultural tractor wheels andtires.

[0063] The axle shaft 80 is formed with a plurality of teeth creating arack 280 on the surface of the shaft. This rack is used with a spurgear, not shown, to move the wheel hub 254 along the length of the axleshaft 80. The clamp mechanism shown in FIG. 13 enables the wheels to beinfinitely adjustable along the axle shaft 80.

[0064] Suspension Hydraulics

[0065] A simplified schematic of the suspension hydraulic system isshown in FIG. 14. An electronic controller 306 controls the extension ofthe cylinder rods 88. The controller 306 operates the solenoids of theleft and right hydraulic valves 308, 310 to direct fluid from the pump312 to the cylinders 82, 84 and back to the reservoir. The extension ofthe rods 88 is measured by left and right rotary potentiometers 314,316. The potentiometers are located on the pivot pin 100 at the couplingof the upper control arm 64 to the inner suspension housing. Thepotentiometers measure the rotational position of the upper control arm,which is proportional to the rod extension. The valves 308, 310 areoperated to extend or retract the rods for level control of the vehiclebased on the vehicle load. Pressure accumulators 318, 320 provide ahydro-pneumatic spring system to the suspension. Multiple accumulatorswith different volumes and pre-loads can also be used.

[0066] A switch 322 is located at the operator's station 18 foractuation by the operator while positioned at the operator's station.The switch manually controls the suspension system to raise or lower thetractor rear end, and thus the hitch, at a relatively slow rate. Theswitch 322 is only operational when the tractor is stopped or moving ata slow speed, such as less than 2 or 3 kph. The switch is useful whenconnecting the tractor to an implement, particularly to the tractordrawbar 324 (FIG. 1). After an implement is unhitched, the jack standoften settles into the ground, lowering the implement tongue height. Theswitch 322 is used to lower the drawbar to a position beneath theimplement tongue so that the implement need not be raised. Afterconnecting the implement, the operator may raise the tractor rear end bythe switch 322 or, if not, the suspension load leveling system willlevel the tractor once the tractor is in motion.

[0067] 4-Wheel Drive Tractors

[0068] An articulated four-wheel drive tractor 290 is shown in FIG. 15.The tractor 290 includes a front and rear portion 292 having a frontdrive axle 296 and a rear portion 294 having a rear drive axle 298. Thefront and rear portions are joined to one another by a coupling 300 toarticulate about an upright axis 302 for steering. This type of 4-wheeldrive tractor is well known. The tractor 290 is a 9000 series 4-wheeldrive tractor available from John Deere.

[0069] The front and rear drive axles 296, 298 are similar to the axleshown in FIG. 2, having a central differential case, inboard planetaryfinal drives and left and right axle housings projecting laterallyoutward to support axle shafts. Both the front and rear drive axles 296,298 can be equipped with the suspension of the present invention. Thelaterally projecting axle housings are replaced with the innersuspension housings of the present invention. The suspension systemincluding the upper and lower control arms and the axle housings aremounted to the inner suspension housings as described above. The axleshafts are driven through the universal joint described above. Theprovision of the suspension axles can improve operator comfort andprovide for faster travel speeds. In addition, by allowing the drivewheels to move up and down relative to the tractor frame, the joint 300can be simplified. The joint will no longer have to allow the front andrear portions of the tractor to roll relative to one another.

[0070] The present invention has been described as having a differentialcase to which the suspension components are attached with the suspensionincluding left and right inner suspension housings rigidly coupled tothe differential case. In a conventional row crop tractor thedifferential case is part of the powertrain that includes the engine,transmission and differential. These components may be mounted to aframe structure to which the front axle and operator's station is thenmounted or they may, themselves, form the vehicle frame structure. Thecontrol arms and hydraulic cylinders may be attached to the differentialcase, the inner suspension housings, the central housing or to thevehicle frame structure. The claim language that follows is thus to bebroadly construed with this in mind.

[0071] While the invention has be described in the context of a wheeledtractor, it is possible to provide the suspended rear drive wheels on atrack driven tractor. This could be either a friction or mechanicaldrive track.

[0072] The drive axle suspension of the present invention provides atractor with a drive axle that is suspended. The suspended axle can beused as the rear axle in a row crop tractor that maintains thecharacteristics of a non-suspended row crop tractor. In addition, thesuspended axle can be used as either the front or the rear axle of anarticulated 4-wheel drive tractor.

[0073] The invention should not be limited to the above-describedembodiment, but should be limited solely by the claims that follow.

We claim:
 1. An agricultural tractor comprising: an engine; atransmission driven by the engine a drive axle driven by thetransmission, the drive axle including a central housing having left andright drive output members, left and right axle housings movably coupledto the central housing for vertical movement of the left and right axlehousings relative to the central housing, left and right axle shaftsrotatably carried by the left and right axle housings and left and rightuniversal joints drivingly coupling the left and right drive outputmembers to the left and right axle shafts respectively; and left andright wheel and tire assemblies coupled to the left and right axleshafts respectively.
 2. The agricultural tractor as defined by claim 1further comprising left and right inboard final drives in the centralaxle housing whereby the left and right drive output members rotate atthe same speed as the left and right axle shafts, respectively.
 3. Theagricultural tractor as defined by claim 2 wherein the output membersare planet carriers of the inboard final drives.
 4. The agriculturaltractor as defined by claim 1 wherein the left and right wheel and tireassemblies are positioned at a 60 inch tread spacing.
 5. Theagricultural tractor as defined by claim 1 further comprising means forinfinitely adjusting the position of the wheel and tire assemblies alongthe left and right axle shafts.
 6. The agricultural tractor as definedby claim 5 wherein the left and right wheel and tire assemblies arepositioned at a 60 inch tread spacing.
 7. The agricultural tractor asdefined by claim 6 wherein the central housing includes left and rightinboard final drives.
 8. The agricultural tractor as defined by claim 6wherein the engine has a power rating of at least 75 kW (100 hp).
 9. Theagricultural tractor as defined by claim 6 wherein the engine has apower rating of at least 124 kW (165 hp).
 10. The agricultural tractoras defined by claim 1 wherein the central housing is part of aagricultural tractor frame.
 11. The agricultural tractor as defined byclaim 10 wherein the left and right axle housings are each coupled tothe central housing by left and right upper and lower control armspivotally coupled to the central housing and the axle housings formovement of the axle housings relative to the central housing and atleast one spring member extending between the frame and the axle housingto resiliently transmit loads from the frame to the axle housings. 12.The agricultural tractor as defined by claim 11 wherein the springmember is a hydraulic cylinder and extendable rod coupled to the centralhousing and to the axle housing, the hydraulic cylinder being connectedin a hydraulic circuit with at least one pressure accumulator.
 13. Theagricultural tractor as defined by claim 11 further comprising a rotarypotentiometer to measure the rotary position of one of the control arms.14. The agricultural tractor as defined by claim 11 wherein the controlarms are coupled to the axle housing by upper and lower ball jointswherein the upper and lower ball joints define an upright axis aboutwhich the axle housing can pivot to turn the wheel and tire assembliesand further comprising a variable length member between the centralhousing and the axle housing to control rotation of the axle housingabout the upright axis.
 15. The agricultural tractor as defined by claim14 wherein the variable length member is a hydraulic cylinder.
 16. Theagricultural tractor as defined by claim 1 wherein the left and rightaxle housings are mechanically separated from one another whereby oneaxle housing can move without causing the other axle housing to movethrough a mechanical coupling.
 17. The agricultural tractor as definedby claim 1 wherein the universal joint comprises: a drive yoke at anoutboard end of the drive output member, the drive yoke defining anoutboard face; a first journal member coupled to the drive yoke forpivotal motion about a first joint pivot axis transverse to alongitudinal axis of the drive output member, the first joint pivot axisbeing inboard of the drive yoke outboard face; a coupling yoke joined tothe first journal member for pivotal motion about a second joint pivotaxis transverse to the longitudinal axis of the drive output member andtransverse to the first joint pivot axis; a driven yoke at an inboardend of the axle shaft, the driven yoke defining an inboard face; asecond journal member coupled to the second yoke for pivotal motionabout a third joint pivot axis transverse to a longitudinal axis of theaxle shaft, the third joint pivot axis being outboard of the driven yokeinboard face; and the second journal member being joined to the couplingyoke for pivotal motion about a fourth joint pivot axis transverse tothe longitudinal axis of the axle shaft and transverse to the thirdjoint pivot axis.
 18. The agricultural tractor as defined by claim 17wherein the outboard face of the drive yoke and the inboard face of thedriven yoke are axially adjacent to one another.
 19. The agriculturaltractor as defined by claim 17 wherein the outboard face of the driveyoke and the inboard face of the driven yoke are axially spaced lessthan one inch from one another.
 20. The agricultural tractor as definedby claim 17 wherein the first journal member is an annular membersurrounding a hub of the central housing.
 21. The agricultural tractoras defined by claim 17 wherein the second journal member is an annularmember surrounding a hub of the axle housing.
 22. The agriculturaltractor as defined by claim 17 further comprising inner bearings carriedby a hub in the central housing and supporting the drive output membertherein, the inner bearings extending axially outward beyond the firstand second joint pivot axes; and outer bearings carried by a hub in theaxle housing and supporting the axle shaft therein, the outer bearingsextending axially inward beyond the third and fourth joint pivot axes.23. The agricultural tractor as defined by claim 1 wherein the universaljoint comprises: an drive yoke at an outboard end of the drive outputmember; an driven yoke at in inboard end of the axle shaft; inboard andoutboard journal members pivotally coupled to the drive and driven yokesrespectively; a coupling yoke pivotally coupled to both the inboard andoutboard journal members; and the inboard and outboard journal membersand the coupling yoke being positioned radially outward of the driveyoke and driven yoke.
 24. The agricultural tractor as defined by claim23 wherein the central housing has an axially extending bearing hubsupporting the drive output member, and the inboard journal memberradially surrounds the bearing hub.
 25. The agricultural tractor asdefined by claim 23 wherein the axle housing has an axially extendingbearing hub supporting the axle shaft, and the outboard journal memberradially surrounds the bearing hub.
 26. An agricultural tractorcomprising: a frame; an engine; a transmission driven by the engine; adrive axle assembly driven by the transmission, the axle assemblyincluding differential case having left and right planetary finaldrives, the final drives having an output member, left and right innersuspension housings fixed to the differential case, left and right upperand lower control arms pivotally coupled to the inner suspensionhousings and extending outward to distal ends, left and right axlehousings pivotally coupled to the distal ends of the control arms for upand down movement of the axle housings relative to the inner suspensionhousings, left and right axle shafts rotatably carried by the left andright axle housings, left and right universal joints drivingly couplingthe output members of the left and right final drives to the left andright axle shafts respectively, and left and right spring membersextending between the left and right inner suspension housings and theleft and right axle housings to resiliently transmit loads from theframe to the axle housings; and left and right wheel and tire assembliescoupled to the left and right axle shafts respectively.
 27. Theagricultural tractor as defined by claim 26 wherein the left and rightwheel and tire assemblies are located on the axle shafts to provide a 60inch tread width.
 28. The agricultural tractor as defined by claim 26wherein the left and right wheel and tire assemblies are adjustable inposition along the left and right axle shafts.
 29. The agriculturaltractor as defined by claim 26 wherein the differential case and theleft and right inner housings are rigidly fixed to and part of theframe.
 30. The agricultural tractor as defined by claim 26 wherein: thecontrol arms are coupled to the inner suspension housings by pins thatdefine upper and lower pivot axes; and the axle housings are coupled tothe distal ends of the control arms by an upper ball joint and a lowerball joint.
 31. The agricultural tractor as defined by claim 30 furthercomprising left and right connecting links extending between the leftand right inner suspension housings and left and right axle housings toprevent rotation of the left and right axle housings about left andright upright axes defined by the left and right upper and lower balljoints.
 32. The agricultural tractor as defined by claim 30 furthercomprising left and right variable length members extending between theleft and right inner housings and left and right axle housings tocontrol rotation of the left and right axle housings about left andright upright axes defined by the left and right upper and lower balljoints to control turning of the left and right wheel and tireassemblies for steering of the tractor.
 33. The agricultural tractor asdefined by claim 32 wherein the variable length member is a hydrauliccylinder.
 34. The agricultural tractor as defined by claim 26 whereinthe left and right spring members include hydraulic cylinders coupled ina hydraulic circuit to one or more pressure accumulators.
 35. Afour-wheel drive agricultural tractor comprising: a front portion havinga front drive axle; a rear portion having a rear drive axle, the frontand rear portions being joined to one another by an articulating jointand both the front and rear drive axle assembly having left and rightwheel and tire assemblies; at least one of the front and rear driveaxles having a central housing having left and right drive outputmembers, left and right axle housings coupled to the central housing forvertical movement of the left and right axle housings relative to thecentral housing, left and right axle shafts rotatably carried by theleft and right axle housings and left and right universal jointsdrivingly coupling the left and right drive output members to the leftand right axle shaft respectively, the wheel and tire assemblies of thedrive axle assembly being mounted to the left and right axle shafts. 36.The agricultural tractor as defined by claim 35 further comprising leftand right inboard final drives in the central axle housing whereby theleft and right drive output members rotate at the same speed as the leftand right axle shafts respectively.
 37. The agricultural tractor asdefined by claim 36 wherein the output members are planet carriers ofthe inboard final drives.
 38. The agricultural tractor as defined byclaim 35 wherein the left and right axle housings are each coupled tothe central housing by upper and lower control arms pivotally coupled tothe inner and axle housings for movement of the axle housings relativeto the central housing and at least one spring member extending betweenthe frame and the axle housing to resiliently transmit loads from theframe to the axle housings.
 39. The agricultural tractor as defined byclaim 35 wherein each universal joint comprises: an drive yoke at anoutboard end of the drive output member; an driven yoke at in inboardend of the axle shaft; inboard and outboard journal members pivotallycoupled to the drive and driven yokes respectively; a coupling yokepivotally coupled to both the inboard and outboard journal members; theinboard and outboard journal members and the coupling yoke beingpositioned radially outward of the drive yoke and driven yoke whereinthe drive yoke and driven yoke are axially adjacent one another.
 40. Auniversal joint for transmitting rotary power: a drive member rotatablysupported in a first housing by a first bearing set for rotation about afirst longitudinal axis; a driven member rotatably supported in a secondhousing by a second bearing set for rotation about a second longitudinalaxis; a drive yoke fixed to the drive member; a first journal membercoupled to the drive yoke for pivotal motion about a first joint pivotaxis transverse to a longitudinal axis of the drive member; a couplingyoke joined to the first journal member for pivotal motion about asecond joint pivot axis transverse to the longitudinal axis of the drivemember and to the first joint pivot axis and lying in the same plane asthe first joint pivot axis; a driven yoke fixed to the driven member; asecond journal member coupled to the driven yoke for pivotal motionabout a third joint pivot axis transverse to the second longitudinalaxis; and the second journal member being joined to the coupling yokefor pivotal motion about a fourth joint pivot axis transverse to thesecond longitudinal axis and to the third joint pivot axis and lying inthe same plane as the third joint pivot axis; and at least a portion ofthe first and second bearing sets being located between the plane of thefirst and second joint pivot axes and the plane of the third and fourthjoint pivot axes.
 41. The universal joint as defined by claims 40wherein the first and second journal members and the coupling yokeradially surround the drive and driven yokes. 42 The universal joint asdefined by claims 40 wherein the first and second journal members areeach two piece members with the two pieces of each journal member joinedtogether along radially extending planes. 43 The universal joint asdefined by claims 40 wherein the coupling yoke is a two piece memberjoined together along an axially extending plane.
 44. A suspended driveaxle for a work vehicle comprising: a differential case having left andright planetary final drives, the final drives having each having anoutput member; left and right inner suspension housings fixed to thedifferential case; left and right upper and lower control arms pivotallycarried by the inner suspension housings and extending outward to distalends; left and right axle housings pivotally coupled to the distal endsof the control arms for up and down movement of the axle housingsrelative to the inner suspension housings; left and right axle shaftsrotatably carried by the left and right axle housings; left and rightuniversal joints drivingly coupling the output members of the left andright final drives to the left and right axle shafts respectively; andleft and right spring members extending between the left and right innersuspension housings and the left and right axle housings to resilientlytransmit loads therebetween.
 45. The drive axle as defined by claim 44wherein: the control arms are coupled to the inner suspension housingsby pins that define upper and lower pivot axes; and the axle housingsare coupled to the distal ends of the control arms by an upper and alower ball joint.
 46. The drive axle as defined by claim 45 furthercomprising left and right connecting links extending between the leftand right inner suspension housings and left and right axle housings toprevent rotation of the left and right axle housings about left andright upright axes defined by the left and right upper and lower balljoints.
 47. The drive axle as defined by claim 45 further comprisingleft and right variable length members extending between the left andright inner housings and left and right axle housings to controlrotation of the left and right axle housings about left and rightupright axes defined by the left and right upper and lower ball jointsto control turning of the left and right wheel and tire assemblies forsteering of the tractor.
 48. The drive axle as defined by claim 47wherein the variable length member is a hydraulic cylinder.
 49. Thedrive axle as defined by claim 44 wherein the left and right springmembers include hydraulic cylinders coupled in a hydraulic circuit toone or more pressure accumulators.
 50. The drive axle as defined byclaim 44 wherein each universal joint comprises: an drive yoke at anoutboard end of the drive output member; an driven yoke at in inboardend of the axle shaft; inboard and outboard journal members pivotallycoupled to the drive and driven yokes respectively; a coupling yokepivotally coupled to both the inboard and outboard journal members; theinboard and outboard journal members and the coupling yoke beingpositioned radially outward of the drive yoke and driven yoke whereinthe drive yoke and driven yoke are axially adjacent one another.
 51. Anagricultural tractor comprising: a frame; an operator's platform; rearwheels; a rear axle carrying the rear wheels and including a suspensionsystem coupling the rear wheels to the frame for vertical motion of therear wheels relative to the frame, the suspension system including ahydro-pneumatic spring system including at least one hydraulic cylinderon each side of the tractor, the extension of the cylinder roddetermining the position of the rear wheels relative to the frame; and aswitch at the operator's platform for actuation by an operator to raiseand lower the rear end of the tractor by extending or retracting thecylinder rod of the hydraulic cylinders.